Acoustic filters are presently utilized in a variety of fluid filled systems, including those aboard U.S. Navy ships, to block, limit or reduce transmission of noise producing acoustic energy within a range of acoustic frequencies. Such filters are however not tunable for use with respect to specific acoustic frequencies. Currently absorptive types of filters are utilized to absorb acoustic energy, while reactive types of filters are utilized to reflect acoustic energy within a certain frequency range back toward its source in order to quiet the piping system downstream of the filter.
A rubber cylinder type of filter is also currently utilized, wherein liquid in a pipe is exposed to a single gas filled cavity. The rubber cylinder component of such a filter breaks up under acoustic frequencies higher than its breathing mode frequency to thereby reduce optimal performance. Such a filter cannot be tuned to a wide range of frequencies so as to adjust it to a specific desired frequency within the range. Such rubber cylinder filters furthermore require tube reinforcement to prevent the rubber cylinder from being sucked into the liquid under high flow conditions within the pipe, and require maintenance cleansing for removal of obstructive particles or silt involving removal of the filter from the pipe. Operational interference also occurs as a result of creepage of the rubber cylinder over time under the weight of the liquid in the pipe.
Another type of available filter involves use of an extension pipe section extending some distance from a main pipe to which it is connected. Such filters are only slightly effective in filtering and are often unsatisfactory in certain installations.
It is therefore an important object of the present invention to provide an acoustic filter which will avoid the aforementioned problems and disadvantages associated with the currently available acoustic filters.